Modulating effect of low level-laser therapy on fibrosis in the repair process of the tibialis anterior muscle in rats.

The treatment of muscle injuries is a common practice at rehabilitation centers. Low-level laser therapy (LLLT) has demonstrated positive effects regarding the modulation of the inflammatory response, the enhancement of the tissue repair process and the prevention of fibrosis. The aim of the present study was to evaluate the effects of LLLT on morphological aspects of muscle tissue, collagen remodeling and activity of matrix metalloproteinase 2 (MMP-2) in rat skeletal muscle following acute injury. Wistar rats were divided into five groups: (1) control group (n = 10), (2) sham group (n = 10), (3) LLLT group (n = 30), (4) non-treated injury group (n = 30) and (5) injury + LLLT group (n = 30). Cryoinjury was performed on the belly of the tibialis anterior (TA) muscle. LLLT was performed daily with an AlGaAs laser (780 nm; beam spot of 0.04 cm(2), output power of 40 mW, power density of 1 W/cm(2), energy density of 10 J/cm(2) and 10-s exposure time). Animals were euthanized at 1, 3 and 7 days. The TA muscles were removed and weighed. Morphological aspects were evaluated using H & E staining. The amount and distribution of collagen fibers were evaluated by picrosirius staining. Characterization and activity of MMP-2 were evaluated by zymography and Western blot techniques, respectively. The results revealed that LLLT induced a reduction in inflammatory infiltrate and myonecrosis after 1 day, an increase in the number of blood vessels after 3 and 7 days as well as an increase in the number of immature muscle fibers and MMP-2 gelatinase activity after 7 days. In conclusion, LLLT has a positive effect on the inflammatory process, MMP2 activity and collagen organization and distribution in the repair process of rat skeletal muscle.